Water polo coach Lilie James was captured chatting with hockey coach Paul Thijssen unaware of the attack he had been plotting to carry out inside the Sydney school where they both worked.
The pair had previously been involved in a casual two-month relationship, but Ms James had ended it five days before her murder on the evening of October 25, 2023.
In CCTV footage shown to an inquest into the pair's deaths on Wednesday, the 21-year-old woman can be seen carrying a swimsuit as she walks towards the gym bathrooms at St Andrew's Cathedral School in the city centre.
She looked at a sign blocking off one of the bathrooms - which the 24-year-old Thijssen had placed there earlier in the evening - before entering the disabled bathroom.
Thijssen followed her and stood outside the bathroom with a hammer in his right hand.
He appeared to look directly at the CCTV camera before lunging into the bathroom two minutes later.
Thijssen bludgeoned her to death with the hammer inside the bathroom in a premeditated attack before he took his own life in the city's eastern suburbs, the inquest was previously told.
Counsel assisting the coroner Jennifer Single SC said Ms James had been smiling and interacting with her ex-lover minutes before her death and there had been no indication of what he was about to do.
"No matter how many times you see that footage, it is not easy to watch," she said as her voice broke.
Security footage from the school from earlier in the evening showed Thijssen practising the attack outside the bathroom by alternating which hand would hold the hammer.
He then could be seen disabling the automatic sliding doors, which Ms Single said indicated that he wanted to prevent the school cleaners from disturbing his assault on the young woman.
The three-day inquest will also examine issues of coercive control and unacceptable behaviour in relationships in an attempt to prevent similar deaths.
Thijssen stalked Ms James for days before he murdered her in a "calculated, premeditated" attack at the school where they both worked, the coroner was earlier told.
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